In biological systems, the functions of light harvesting, electron transfer and energy transfer are performed by a variety of prosthetic groups. In the photosynthetic systems of higher plants and cyanobacteria,1 light harvesting chromophores funnel light energy via Forster transfer to a specialized chlorophyll species where charge separation occurs; subsequent electron transfer through a series of redox active cofactors eventually oxidizes water and reduces NADP+. Concomitant proton translocation across the membrane generates an electrochemical potential that drives ATP synthesis. These processes require the interaction of light harvesting species, redox active cofactors and amino acids in the protein environment. in E. coli, DNA damaged by UV radiation undergoes repair of lethal pyrimidine dimers by an enzyme known as photolyase2 by utilizing visible light in a similar manner. The light harvesting function in this system is fulfilled by a folate compound, while repair of the dimers is thought to occur via electron transfer from a flavin. in this proposal, we plan to use solid state nuclear magnetic resonance techniques (SSNMR) to characterize the -photo-chemically induced dynamic nuclear polarization (CIDNP) signals from Photosystem I (PSI) and photolyase and utilize them to investigate the relationship between structure and function of-the prosthetic groups involved in biological electron transfer. This relationship will be used to elucidate and confirm the mechanisms by which these electron transfer and energy transduction processes transpire.